sequenceDiagram
    participant A as Seller
    participant EA as Escrow A (sell)
    participant X as MEX operator/engine
    participant EB as Escrow B (buy)
    participant B as Buyer
    A->>EA: 1. createOrder — lock sellToken (rate fixed)
    B->>EB: 1. createOrder — lock buyToken (rate fixed)
    X->>EA: 2. settleMatch — cross the two prefunded escrows
    X->>EB: settleMatch
    EA-->>EB: sellToken to buyer
    EB-->>EA: buyToken to seller
    Note over EA,EB: each escrow checks ITS own rate; fee ≤ 1% to treasury
    A->>EA: 3. withdraw()
    B->>EB: 3. withdraw()